A test of niche centrality as a determinant of population trends and conservation status in threatened and endangered North American birds

Abstract

Abundance and other aspects of population ecology have long been known to con- tribute to shaping the geography of species' distributions. In particular, abundance patterns have recently been shown to negatively correlate with environmental distance from conditions in the center of a species' abiotic niche, rather than vary with distance from the geographic center of a species' distribution. We tested for such associations across 8 species of endangered or threatened bird species in North America using population trend data derived from >4 decades of North Amer- ican Breeding Bird Surveys. Although we found no consistent overall pattern, we did observe nega- tive population trends at conditions that were the most extreme within species' niches. This suggests that niche peripherality is a relevant factor to consider in conservation planning. Specifi- cally, environmentally peripheral sites may be poor places in which to protect populations of endan- gered and threatened species, irrespective of how centrally they may occur within species' geo- graphic distributions.